Fuel cell system and controlling method thereof

ABSTRACT

A fuel cell system comprises: a fuel storage means for storing a fuel; a direct borohydride fuel cell (DBFC); a fuel circulation supply means for circulation and supplying a fuel to an anode of the DBFC from the fuel storage means; a polymer electrolyte membrane fuel cell (PEMFC) for receiving hydrogen generated at the anode of the DBFC as a fuel; a hydrogen control means for controlling hydrogen generated from the anode of the DBFC in correspondence to an amount required by the PEMFC and thereby supplying the hydrogen to the PEMFC; and an air supply means for supplying air to a cathode of the DBFC and an cathode of the PEMFC.

TECHNICAL FIELD

The present invention relates to a fuel cell system and a controllingmethod thereof, and more particularly, to a fuel cell system capable ofmaximizing an output of electric energy and enhancing a stability of asystem by efficiently using a fuel, and a controlling method thereof.

BACKGROUND ART

A fuel cell is being developed as a replacement of a fossil fuel that isnot eco-friendly. The fuel cell is a generating device for directlyconverting chemical energy into electric energy. A hydrogen-includingfuel and an oxygen-including air are continuously supplied to the fuelcell, in which the hydrogen and the oxygen are electrochemically reactedto each other. The fuel cell directly converts an energy differencebetween before the reaction and after the reaction into electric energy.The fuel cell is continuously provided with a fuel and oxygen thereby tocontinuously generate electric energy.

The fuel cell includes a phosphoric acid fuel cell, an alkaline fuelcell, a proton exchange membrane fuel cell, a molten carbonate fuelcell, a solid oxide fuel cell, a direct methanol fuel cell, etc. Saidfuel cells are operated by the same principle, and are classifiedaccording to a kind of a used fuel, a driving temperature, a catalyst,etc.

Also, the fuel cell is being developed to be applied variously as adomestic fuel cell for supplying electricity to a home, a fuel cell usedin an electricity car, a fuel cell used in a mobile terminal or anotebook computer, a fuel cell movable at home and supplyingelectricity, etc.

Especially, a fuel cell for operating home electronics or other electricdevices by being moved at home or at an outdoors has to be minimized inorder to be conveniently portable, and has to maximize an output ofelectric energy under a state that the size thereof is limited. Also, astability of the fuel cell has to be obtained.

DISCLOSURE OF INVENTION

Therefore, it is an object of the present invention to provide a fuelcell system capable of maximizing an output of electric energy andhaving a compactification of an entire structure by efficiently using afuel, and a controlling method thereof.

Another object of the present invention is to provide a fuel cell systemcapable of enhancing a stability of a system.

To achieve these objects, there is provided a fuel cell systemcomprising: a fuel storage means for storing a fuel; a DBFC; a fuelcirculation supply means for circulation-supplying a fuel to an anode ofthe DBFC from the fuel storage means; a PEMFC for receiving hydrogengenerated from the anode of the DBFC as a fuel; a hydrogen control meansfor controlling hydrogen generated from the anode of the DBFC incorrespondence to an amount required by the PEMFC and thereby supplyingthe hydrogen to the PEMFC; and an air supply means for supplying air toa cathode of the DBFC and a cathode of the PEMFC.

To achieve these objects, there is also provided a method forcontrolling a fuel cell system comprising the steps of: driving a DBFC;controlling hydrogen, a byproduct generated at an anode of the DBFCafter a reaction as a preset amount; and driving a PEMFC by receivinghydrogen having an amount set in the hydrogen controlling step and thusby using the hydrogen as a fuel.

DESCRIPTION OF DRAWINGS

FIG. 1 is a piping diagram showing one embodiment of a fuel cell systemaccording to the present invention;

FIG. 2 is a flow chart showing a controlling method of a fuel cellsystem according to the present invention;

FIG. 3 is a flow chart showing a step of driving a DBFC in thecontrolling method of a fuel cell system according to the presentinvention;

FIG. 4 is a flow chart showing a step of controlling a generation ofhydrogen in the controlling method of a fuel cell system according tothe present invention;

FIGS. 5 and 6 are flow charts respectively showing a step of controllinghydrogen in the controlling method of a fuel cell system according tothe present invention;

FIG. 7 is a flow chart showing a safe control algorithm in thecontrolling method of a fuel cell system according to the presentinvention; and

FIG. 8 is a flow chart showing a step of stopping the system in thecontrolling method of a fuel cell system according to the presentinvention.

BEST MODE

Hereinafter, a fuel cell system according to the present invention willbe explained with reference to the attached drawings.

FIG. 1 is a piping diagram showing one embodiment of a fuel cell systemaccording to the present invention.

As shown, the fuel cell system according to the present inventioncomprises: a fuel storage means for storing a fuel 100; a DBFC 200; afuel circulation supply means 300 for circulation-supplying a fuel fromthe fuel storage means 100 to an anode of the DBFC 200; a PEMFC 400 forreceiving hydrogen generated from the anode of the DBFC 200 as a fuel; ahydrogen control means 500 for controlling hydrogen generated from theanode of the DBFC 200 in correspondence to an amount required by thePEMFC 400 and thereby supplying the hydrogen to the PEMFC 400; and anair supply means 600 for supplying air to a cathode of the DBFC 200 anda cathode of the PEMFC 400.

The fuel storage means 100 includes: a fuel tank 110 for inputting apower fuel and water; and an electrolyte reservoir 120 for containingelectrolyte aqueous solution. As the power, one of NaBH₄, KBH₄, LiAlH₄,KH, NaH, etc. is used. Also, as the electrolyte aqueous solution, one ofKOH and NaOH is used.

The DBFC 200 includes: an anode where a fuel is electrochemicallyoxidized; and a cathode where ion oxidized in the anode and oxygen inthe air are electrochemically deoxidized. The DBFC 200 has a well-knowngeneral structure.

The fuel circulation supply means 300 includes: a first line 310 forconnecting the fuel tank 110 and the anode of the DBFC 200; a gas/liquidseparator 320 for separating a byproduct generated at the anode of theDBFC 200 after a reaction into gas and liquid; a second line 330 forconnecting the gas/liquid separator 320 and the fuel tank 110 andthereby guiding a liquid byproduct of the gas/liquid separator 320 tothe fuel tank 110; a fuel pump 340 mounted at the first line 310; arecycle pump 350 mounted at the second line 330; and an electrolytesupply means for supplying an electrolyte to the anode of the DBFC 200.

The second line 330 positioned between the recycle pump 350 and the fueltank 110 is provided with a first valve 360 for preventing a fluid ofthe fuel tank 110 from backwardly flowing to the gas/liquid separator320 when the recycle pump 350 is stopped.

A filter (not shown) for filtering a solidified byproduct is mounted atthe second line 330 or at the fuel tank 110.

The electrolyte supply means includes: a third line 371 for connectingthe electrolyte reservoir 120 and the first line 310; a three-way valve372 mounted at a portion that the first line 310 and the third line 371are connected to each other, for controlling a flow direction of afluid; and a fourth line 373 for connecting an outlet of the cathode ofthe DBFC 200 and the electrolyte reservoir 120.

One side of the third line 371 is connected to the first line 310positioned between the DBFC 200 and the fuel pump 340 at an arbitraryposition. Another side of the third line 371 is connected to a lowersurface of the electrolyte reservoir 120. Also, one side of the fourthline 373 is connected to an upper portion of the electrolyte reservoir120.

A first discharge line 374 for discharging gas contained in theelectrolyte reservoir 120 is connected to an upper portion of theelectrolyte reservoir 120. Also, a first purge valve 375 for controllingan inner pressure of the electrolyte reservoir 120 by opening andclosing the first discharge line 374 is provided at the upper portion ofthe electrolyte reservoir 120. When a water level of liquid contained inthe electrolyte reservoir 120 is more than a preset value, the firstpurge valve 375 is closed thus to close the electrolyte reservoir 120.As the electrolyte reservoir 120 is closed, an inner pressure thereof isincreased by gas contained therein. Also, by the inner pressure, theliquid contained in the electrolyte reservoir 120 is discharged throughthe third line 371.

As a modification example of the fuel storage means 100, the electrolyte120 and the fuel tank 110 can be constituted as one, in which a powerfuel, water, and the electrolyte aqueous solution can be contained.

The PEMFC 400 is composed of: an anode where hydrogen generated from theDBFC 200 is electrochemically oxidized; and a cathode where ion oxidizedin the anode and oxygen in the air are electrochemically deoxidized. ThePEMFC 400 has a well-known general structure.

The hydrogen control means 500 includes: a connection line 510 forconnecting a gas/liquid separator 320 constituting the fuel circulationsupply means 300 and the anode of the PEMFC 400, and flowing hydrogengenerated after a reaction to the PEMFC 400; a hydrogen reservoir 520mounted at the connection line 510, for temporarily storing hydrogen; amain gas valve unit mounted at the connection line 510 between thehydrogen reservoir 520 and the PEMFC 400, for controlling a hydrogenpressure as a certain degree so that hydrogen of the hydrogen reservoir520 can be supplied to the cathode of the PEMFC 400 with a certainamount; and a hydrogen conduit open/close unit for allowing/shielding ahydrogen flow into the hydrogen reservoir 520 by a pressure differencebetween inside of the connection line 510 positioned at an inlet of thehydrogen reservoir 520 and inside of the connection line 510 positionedat an outlet of the hydrogen reservoir 520.

The hydrogen conduit open/close unit includes: a first pressure sensor531 mounted at the connection line 510 positioned between the gas/liquidseparator 320 and the hydrogen reservoir 520, for sensing a pressure; asecond pressure sensor 532 mounted at the connection line 510 betweenthe main gas valve unit and the hydrogen reservoir 520, for sensing apressure; a second valve 533 mounted at the connection line 510 betweenthe first pressure sensor 531 and the hydrogen reservoir 520, forcontrolling hydrogen flowing in the connection line 510; and a controlmeans (not shown) for opening and closing the second valve 533 by apressure difference detected by the first and second pressure sensors531 and 532.

The connection line 510 positioned between the first pressure sensor 531and the second valve 533 can be provided with a first compressor 534 forcompression-pumping hydrogen.

The main gas valve unit includes: a third valve 541 mounted at theconnection line 510 between the hydrogen reservoir 520 and the PEMFC400, for controlling a flow amount of hydrogen; a regulator 542 mountedat the connection line 510 between the third valve 541 and the PEMFC400, for supplying hydrogen of a certain pressure to the anode of thePEMFC 400; a second discharge line 543 connected to the connection line510 between the hydrogen reservoir 520 and the third valve 541; and arelief valve 544 mounted at the second discharge line 543, fordischarging a pressure outwardly when an excessive pressure is applied.

A third discharge line 411 for discharging a byproduct after a reactionis connected to an outlet of the anode of the PEMFC 400, and a secondpurge valve 412 is mounted at the third discharge line 411.

The air supply means 600 includes: an air distributor 610 fordistributing air; a first distribution line 620 for connecting the airdistributor 610 and the cathode of the DBFC 200; a second distributeline 630 for connecting the air distributor 610 and the cathode of thePEMFC 400; an air introducing line 640 connected to the air distributor610, for introducing external air to the air distributor 610; a secondcompressor 650 mounted at the air introducing line 640, forcompression-pumping external air; and an air filter 660 mounted at theair introducing line 640, for filtering introduced air.

A fourth discharge line 431 for discharging a byproduct generated at thecathode after a reaction is connected to an outlet of the cathode of thePEMFC 400. Also, a humidity exchanger 432 for performing a humidityexchange between air introduced into the cathode and a byproductdischarged to outside is connected between the fourth discharge line 431and the second distribution line 630.

An evaporator 433 for evaporating water discharged from the fourthdischarge line 431 is provided at the fourth discharge line 431. Theevaporator 433 also evaporates water discharged from the first dischargeline 374.

A humidity supply means 670 for supplying humidity to air introducedinto the first distribution line 620 is provided at the firstdistribution line 620. The humidity supply means 670 provided with anadditional water tank (not shown) and a humidifier (not shown) can bemounted at the first distribution line 620. Also, as the humidity means670, the humidity exchanger 432 can be connected to the firstdistribution line 620.

An unexplained reference numeral 220 denotes a cooling fan of the DBFC,and 420 denotes a cooling fan of the PEMFC.

FIG. 2 is a flow chart showing a controlling method of a fuel cellsystem according to the present invention, in which the same referencenumerals were given to the same parts as those of FIG. 1.

As shown, the method for controlling a fuel cell system according to thepresent invention comprises the steps of: driving a DBFC 200;controlling hydrogen that is a byproduct generated at an anode of theDBFC 200 after a reaction as a preset amount; and driving a PEMFC 400 byreceiving hydrogen having an amount set in the hydrogen controlling stepand thus by using the hydrogen as a fuel.

As shown in FIG. 3, in the step of driving a DBFC, the step of supplyinga fuel to an anode of the DBFC 200 includes the steps of: making a fuelof an aqueous solution in a fuel tank 110 by injecting a power fuel andwater thereto; containing electrolyte aqueous solution in an electrolytereservoir 120; pumping the fuel of an aqueous solution and therebysupplying to the anode of the DBFC 200 with the electrolyte aqueoussolution; separating a byproduct generated at the anode after a reactioninto gas and liquid; and pumping the separated liquid and therebycirculation-supplying to the fuel tank 110.

The step of containing an electrolyte in the electrolyte reservoir 120can be performed prior to the step of containing a fuel in the fuel tank110. As the fuel, one of NaBH₄, KBH₄, LiAlH₄, KH, NaH, etc. is used.Also, as the electrolyte aqueous solution, one of KOH and NaOH is used.

In the step of driving the DBFC 200, a byproduct generated at a cathodeof the DBFC 200 after a reaction is supplied to the electrolytereservoir 120 thus to be separated into gas and liquid. Also, theelectrolyte of the electrolyte reservoir 120 is supplied to the anode ofthe DBFC when the DBFC is operated, and closes the electrolyte reservoir120 when the DBFC is stopped. As the electrolyte reservoir 120 isclosed, the byproduct contained in the electrolyte reservoir 120 isintroduced into the fuel tank 110 by a pressure of the electrolytereservoir 120.

Also, when a water level of liquid contained in the electrolytereservoir 120 is more than a preset value, a flow conduit of theelectrolyte aqueous solution is converted by controlling a direction ofa three-way valve 372 thus to forcibly introduce the liquid of theelectrolyte reservoir 120 into the fuel tank 110.

External air is introduced into one conduit and then the air conduit isdiverged into two conduits, through which air is respectively suppliedto the cathode of the DBFC 200 and the cathode of the PEMFC 400.

In the step of driving the DBFC 200, an amount of hydrogen generated atthe cathode of the DBFC 200 after a reaction can be controlled by asupply amount of a fuel supplied to the anode. That is, as shown in FIG.4, a pressure of hydrogen generated at the DBFC 200 is measured. If themeasured pressure is less than a first preset value K1, a fuel iscontinuously supplied to the anode of the DBFC 200. Also, if themeasured value is more than a second preset value K2 greater than thefirst preset value K1, a fuel supply to the anode of the DBFC 200 isstopped and then the hydrogen is purged. Also, if the measured value isbetween the first preset value K1 and the second preset value K2, ahydrogen supply is stopped. The hydrogen supply is performed by a fuelpump 340.

A hydrogen amount generated at the DBFC 200 is influenced by atemperature of a stack constituting the anode and the cathode of theDBFC 200 and a fuel concentration. Therefore, in the conventional art, ahydrogen generation amount was controlled by cooling the stack by a fan,which was not performed fast. According to this, in the presentinvention, a hydrogen generation amount is controlled by controlling apumping amount of the fuel pump 340 for supplying hydrogen to the anodeof the DBFC 200, thereby controlling a hydrogen generation amount fastand thus enhancing a system stability.

As shown in FIG. 5, the step of controlling hydrogen includes the stepsof: respectively measuring an inlet pressure P1 and an outlet pressureP2 of a hydrogen reservoir 520, the inlet for introducing hydrogengenerated at the anode of the DBFC 200 and the outlet for supplying theintroduced hydrogen to the anode of the PEMFC 400; comparing the inletpressure P1 with the outlet pressure P2; continuously supplying hydrogengenerated at the anode of the DBFC 200 to the hydrogen reservoir 520 byopening a second valve 533 for opening and closing a hydrogen conduitwhen the P1 is greater than the P2, and shielding a hydrogen supply tothe hydrogen reservoir 520 when the P1 is less than the P2.

As shown in FIG. 6, the step of controlling hydrogen includes the stepsof: measuring the outlet pressure P2 of the hydrogen reservoir 520, theoutlet for supplying hydrogen generated at the anode of the DBFC 200 andintroduced into the inlet of the hydrogen reservoir to the anode of thePEMFC 400; and measuring a purge cell voltage (PCV) of the PEMFC 400.When the outlet P2 is less than a preset value A1, a hydrogen supplyfrom the hydrogen reservoir 520 to the PEMFC 400 is shielded by closinga third valve 541 for opening and closing a hydrogen conduit for flowinghydrogen from the hydrogen reservoir 520 to the PEMFC 400. Also, whenthe outlet pressure P2 is more than the preset value A1, a value V ofthe PCV is compared with a preset value B1. If the value V of the PCV isgreater than the preset value B1, a hydrogen supply from the hydrogenreservoir 520 to the PEMFC 400 is shielded. Also, when the value V ofthe PCV is less than or the same as the preset value B1, a hydrogensupply from the hydrogen reservoir 520 to the PEMFC 400 is shieldedafter a preset time T1 lapses.

The fuel cell system is provided with a sensor for sensing an oxygenconcentration and a hydrogen concentration, thereby measuring an oxygenconcentration and a hydrogen concentration during an operation thereof.Also, a charged value of a supplementary battery for charging electricenergy is measured. By measuring the oxygen concentration, the hydrogenconcentration, and the charged value of the supplementary battery, astability of the system is increased.

FIG. 7 is a view showing one embodiment of a method for enhancing asystem stability by measuring an oxygen concentration, a hydrogenconcentration, and a charged value of the supplementary battery.

Referring to FIG. 7, a hydrogen concentration is set on the basis of afirst preset value C1 and a second preset value C2 greater than the C1,and an oxygen concentration is set on the basis of a first preset valueD1 and a second preset value D2 less than the D1. Also, a preset chargedvalue E1 of the supplementary battery is defined. Then, a hydrogenconcentration is measured thus to be judged whether the measured valueis more than the C1 or more than the C2, and an oxygen concentration ismeasured thus to be judged whether the measured value is more than theD1 or more than the D2. Also, a charged value of the supplementarybattery is measured thus to be compared with the preset value E1.According to a dangerous degree of the measured value, a warning isperformed visually or auditorily, or the system is stopped.

Another example, the oxygen concentration and the hydrogen concentrationare respectively measured. When the measured oxygen concentration isless than the first preset value, a warning is performed visually orauditorily, and when the measured oxygen concentration is less than thesecond preset value, the system is stopped. Also, when the hydrogenconcentration is more than the first preset value, a warning isperformed visually or auditorily, and when the measured hydrogenconcentration is more than the second preset value, the system isstopped.

Then, a charged value of the supplementary battery is additionallymeasured. When the measured value is more than the preset value E1, acharging is stopped. The charged value of the battery can be judged onthe basis of two preset values.

As shown in FIG. 8, the step of stopping the fuel cell system duringoperation includes the steps of: stopping the DBFC 200 and driving thePEMFC 400 by hydrogen remaining between the DBFC 200 and the PEMFC 400;purge-driving for recollecting a fuel, a byproduct, etc. remainingbetween the DBFC 200 and the fuel tank 110 to the fuel tank 110 byelectric energy generated from the PEMFC 400; continuously driving thePEMFC 400 when a measured amount of hydrogen remaining between the DBFC200 and the PEMFC 400 is more than a preset value and charging thesupplementary battery with the electric energy, and stopping the PEMFC400 when the measured amount of hydrogen is less than or the same as thepreset value.

In the step of stopping the PEMFC 400, the PEMFC 400 is stopped afterbeing generated for a preset time in order to completely consume theremaining hydrogen.

When the purge-driving is not completely performed due to a deficiencyof remaining hydrogen while the PEMFC is operated, the supplementarybattery is used.

Hereinafter, the fuel cell system and the controlling method thereofaccording to the present invention will be explained as follows.

First, a fuel and electrolyte aqueous solution are respectively suppliedto the anode of the DBFC 200 from the fuel tank 110 and the electrolytereservoir 120 constituting the fuel storage means 100. At the same time,as the second compressor 650 constituting the air supply means 600 isoperated, external air is supplied to the cathode of the DBFC 200.Herein, a fuel of the fuel tank 110 is supplied to the anode through thefirst line 310, and the electrolyte aqueous solution is supplied to theanode through the third line 371, the three-way valve 372, and the firstline 310. The external air is supplied to the cathode through the firstdistribution line 620 via the air filter 660 and the air distributor610.

The fuel and the air respectively supplied to the anode of the cathodeof the DBFC 200 are electrochemically reacted thus to generate electricenergy at the DBFC 200. After the reaction, a byproduct includinghydrogen is generated at the anode, and a byproduct includingelectrolyte aqueous solution is generated at the cathode.

The hydrogen-including byproduct generated at the anode is separatedinto hydrogen and liquid by the gas/liquid separator 320, and theseparated liquid is introduced into the fuel tank 110 through the secondline 330 by a pumping force of the recycle pump 350. Also, the separatedhydrogen is supplied to the PEMFC 400 through the connection line 510.

The electrolyte aqueous solution-including byproduct is introduced intothe electrolyte reservoir 120 through the fourth line 373.

In said process, a circulation supply of the fuel is repeated thereby togenerate electric energy at the DBFC 200.

An amount of the hydrogen generated at the anode of the DBFC 200 andsupplied to the PEMFC 400 through the connection line 510 is controlledby the hydrogen control means in correspondence of an amount required bythe PEMFC 400, thereby being supplied to the anode of the PEMFC 400.Said process will be explained in more detail as follows.

First, hydrogen generated at the anode of the DBFC 200 is stored in thehydrogen reservoir 520 through the connection line 510, and the storedhydrogen is supplied to the anode of the PEMFC 400 through theconnection line 510. In said process, the first pressure sensor 531 andthe second pressure sensor 532 respectively positioned at the inlet andthe outlet of the hydrogen reservoir 520 respectively check a pressureof the inlet of the hydrogen reservoir 520 and a pressure of the outletof the hydrogen reservoir 520. When a pressure detected by the firstpressure sensor 531 is greater than a pressure detected by the secondpressure sensor 532, the second valve 533 is opened. On the contrary,when a pressure detected by the first pressure sensor 531 is less than apressure detected by the second pressure sensor 532, the second valve533 is closed. According to this, hydrogen inside the hydrogen reservoir520 is prevented from flowing into the DBFC 200.

When a pressure of the second pressure sensor 532 positioned at theoutlet of the hydrogen reservoir 520 is less than a preset value, thethird valve 541 is closed. On the contrary, a pressure of the secondpressure sensor 532 is more than a preset value, the third valve 541 isopened. Under this state, a PCV of the PEMFC 400 is measured. If themeasured PCV is greater than a preset value, the third valve 541 isclosed thus to shield a hydrogen supply from the hydrogen reservoir 520to the PEMFC 400. On the contrary, if the measure PCV is less than orthe same as a preset value, the third valve 541 is closed after a presettime lapses.

As said process is repeated, hydrogen generated at the DBFC 200 isconstantly and stably supplied to the anode of the PEMFC 400.

The PEMFC 400 generates electric energy as hydrogen supplied to theanode and external air supplied to the cathode are electrochemicallyreacted. The external air is supplied to the cathode by the air supplymeans 600. External air is supplied to the DBFC 200 and the PEMFC 400 bythe air supply means 600.

Electric energy generated at the DBFC 200 and the PEMFC 400 is suppliedto a load or is stored.

The step of stopping the fuel cell system is as follows.

First, a driving of the DBFC 200 is stopped, and a fuel and a productremaining at an inner side of the DBFC 200 and at the fuel circulationsupply means are purged to the fuel tank 110. That is, the driving ofthe DBFC 200 is stopped, and then the recycle pump 350 is continuouslyoperated thus to introduce liquid remaining at the gas/liquid separator320 into the fuel tank 110. Then, the three-way valve 372 is controlledthus to connect the third line 371 and the fuel tank 110, and the firstpurge valve 375 of the hydrogen reservoir 520 is closed thus to increasean inner pressure of the hydrogen reservoir 520. By the increased innerpressure, liquid remaining at the hydrogen reservoir 520 is purged tothe fuel tank 110. The first purge valve 375 is opened under a generaloperation state.

The liquid remaining at the hydrogen reservoir 520 is purged to the fueltank 110 by reversely rotating the fuel pump 340.

If a fuel or a byproduct remains at the electrolyte reservoir 120 or atthe fuel circulation supply means, the fuel or byproduct are solidifiedin the fuel circulation supply means according to a temperature changethereby to lower an efficiency of the system.

When only the PEMFC 400 is operated under a state that the driving ofthe DBFC 200 is stopped, the PEMFC 400 is operated by using hydrogenremaining at the connection line 510 and the hydrogen reservoir 520 as afuel. As the driving of the DBFC 200 is stopped and then the PEMFC 400is operated, electric energy is generated and thereby the recycle pump350 and the fuel pump 340 are operated. According to this, liquidremaining at the electrolyte reservoir 120 or the fuel circulationsupply means is purged, and components constituting the air supply means600 are operated.

If hydrogen remaining at the connection line 510 or the hydrogenreservoir 520 was completely consumed at the PEMFC 400 and therebyelectric energy for performing a purge driving or operating othercomponents is deficient, electric energy stored in the supplementarybattery is used.

When the purge driving is completed, the entire driving is stopped.

As the entire driving is stopped by the above process, hydrogengenerated at the DBFC 200 can be utilized as maximum as possible andsolidified foreign materials do not exist in the system thereby tomaintain a function of the system.

In the method for controlling the fuel cell system, an oxygenconcentration and a hydrogen concentration of a space where the systemis installed are measured. If the measured concentration is more than apreset value, a warning is displayed. According to this, a danger that auser is suffocated due to an oxygen deficiency or an accident is causeddue to a high hydrogen concentration can be prevented, thereby enhancinga stability of the system. Also, when the supplementary battery forcharging a part of electric energy generated at the fuel cell system isexcessively charged, a warning is displayed thus to take a properreaction and thereby the stability of the system is more enhanced.

In the fuel cell system of the present invention, the electrolytereservoir 120 and the first line 310 are connected by the third line371, thereby supplying electrolyte aqueous solution to a fuel suppliedto the anode of the DBFC 200 through the first line 310 during theoperation or purging aqueous solution of the electrolyte reservoir 120to the fuel tank 110 through the first line 310 at the time of stoppingthe driving. According to this, the structure of the fuel circulationsupply means 300 is simplified, and the structure of the inlet/outlet ofthe fuel tank 110 is simplified.

INDUSTRIAL APPLICABILITY

As aforementioned, in the fuel cell system and the controlling methodthereof according to the present invention, a fuel of the DBFC iscirculation-supplied thus to maximize a fuel usage. Also, since hydrogengenerated at the anode of the DBFC is used as a fuel source of thePEMFC, an efficiency of electric energy outputted from the system basedon a fuel supplied to the system is increased and the entire system ismore simplified.

Additionally, since a pressure and an amount of hydrogen generated atthe anode of the DBFC are controlled by the hydrogen control means incorrespondence to a pressure and an amount required by the PEMFC thus tobe supplied to the PEMFC, the system is operated more stably andeffectively and the stability of the system is enhanced.

Also, since the DBFC and the PEMFC are sequentially stopped at the timeof stopping the entire system, hydrogen remaining in the system exceptthe fuel tank is utilized as maximum as possible thus to perform apurge-driving of the system. Therefore, a fuel usage amount is minimizedand a system efficiency is increased.

Additionally, since an oxygen concentration and a hydrogen concentrationare measured thus to be informed to the user while the system isoperated and an excessive charge of electric energy is prevented, theuser's safety is more increased.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover modifications and variationsof this invention provided they come within the scope of the appendedclaims and their equivalents.

1. A fuel cell system comprising: a fuel storage means for storing afuel; a DBFC; a fuel circulation supply means for circulation-supplyinga fuel to an anode of the DBFC from the fuel storage means; a PEMFCreceiving hydrogen generated from the anode of the DBFC as a fuel; ahydrogen control means for controlling hydrogen generated from the anodeof the DBFC in correspondence to an amount required by the PEMFC andthereby supplying the hydrogen to the PEMFC; and an air supply means forsupplying air to a cathode of the DBFC and a cathode of the PEMFC. 2.The system of claim 1, wherein the fuel storage means includes: a fueltank where a power fuel and water are contained; and an electrolytereservoir for containing an electrolyte aqueous solution.
 3. The systemof claim 1, wherein the fuel tank is a single tank in which a powerfuel, water, and the electrolyte aqueous solution are contained.
 4. Thesystem of claim 2, wherein the fuel circulation supply means furthercomprises: a first line for connecting the fuel tank and the anode ofthe DBFC; a gas/liquid separator for separating a byproduct generated atthe anode of the DBFC after a reaction into gas and liquid; a secondline for connecting the gas/liquid separator and the fuel tank andthereby guiding a liquid byproduct of the gas/liquid separator to thefuel tank; a fuel pump mounted at the first line; a recycle pump mountedat the second line; a first discharge line connected to the electrolytereservoir for discharging gas contained in the electrolyte reservoir,and a first purge valve provided at the first discharge line to open andclose the first discharge line; and an electrolyte supply means forsupplying an electrolyte to the anode of the DBFC.
 5. The system ofclaim 4, wherein the electrolyte supply means includes: a third line forconnecting the electrolyte reservoir and the first line; a three-wayvalve mounted at a portion that the first line and the third line areconnected to each other, for controlling a flow direction of a fluid;and a fourth line for connecting an outlet of the cathode of the DBFCand the electrolyte reservoir.
 6. The system of claim 4, wherein thesecond line is provided with a first valve for preventing a fuel of thefuel tank from backwardly flowing to the gas/liquid separator.
 7. Thesystem of claim 4, wherein the second line is provided with a filter forfiltering a solidified by product.
 8. The system of claim 2, wherein thepower fuel is one of NaBH₄ or KBH₄, and the electrolyte aqueous solutionincludes one of NaOH or KOH.
 9. The system of claim 6, wherein thehydrogen control means includes: a connection line for connecting agas/liquid separator constituting the fuel circulation supply means andthe anode of the PEMFC, and flowing hydrogen generated at the DBFC aftera reaction to the PEMFC; a hydrogen reservoir connected to theconnection line, for temporarily storing hydrogen that flows through theconnection line; a main gas valve unit mounted at the connection linebetween the hydrogen reservoir and the PEMFC, for controlling a hydrogenpressure as a certain degree so that hydrogen of the hydrogen reservoircan be supplied to the cathode of the PEMFC with a certain amount; and ahydrogen conduit open/close unit for allowing/shielding a hydrogen flowinto the hydrogen reservoir by a pressure difference between inside ofthe connection line positioned at an inlet of the hydrogen reservoir andinside of the connection line positioned at an outlet of the hydrogenreservoir.
 10. The system of claim 9, wherein the hydrogen conduitopen/close unit includes: a first pressure sensor mounted at theconnection line positioned between the gas/liquid separator and thehydrogen reservoir, for sensing a pressure; a second pressure sensormounted at the connection line between the main gas valve unit and thehydrogen reservoir, for sensing a pressure; a second valve mounted atthe connection line between the first pressure sensor and the hydrogenreservoir, for controlling hydrogen flowing in the connection line; anda control means for opening and closing the second valve by a pressuredifference detected by the first and second pressure sensors.
 11. Thesystem of claim 10, further comprising a compressor provided at theconnection line positioned between the first pressure sensor and thesecond valve, the first compressor for compression-pumping hydrogen. 12.The system of claim 10, wherein the main gas valve unit includes: athird valve mounted at the connection line between the hydrogenreservoir and the PEMFC, for controlling a flow amount of hydrogen; aregulator mounted at the connection line between the third valve and thePEMFC, for supplying hydrogen of a certain pressure to the anode of thePEMFC; a second discharge line connected to the connection line betweenthe hydrogen reservoir and the third valve; and a relief valve mountedat the second discharge line, for controlling a pressure when anexcessive pressure is applied.
 13. The system of claim 12, wherein athird discharge line for discharging a byproduct after a reaction isconnected to an outlet of the anode of the PEMFC, and a second purgevalve is mounted at the third discharge line.
 14. The system of claim 1,wherein the air supply means includes: an air distributor fordistributing air; a first distribution line for connecting the airdistributor and the cathode of the DBFC; a second distribution line forconnecting the air distributor and the cathode of the PEMFC; an airintroducing line connected to the air distributor, for introducingexternal air to the air distributor; an external air compressor mountedat the air introducing line, for compression-pumping external air; andan air filter mounted at the air introducing line, for filteringintroduced air.
 15. The system of claim 13, wherein the PEMFC isprovided with a fourth discharge line at an outlet of the cathodethereof, the fourth discharge line for discharging a byproduct generatedat the cathode after a reaction outwardly, and a humidity exchanger forperforming a humidity exchange between air introduced into the cathodeand a byproduct discharged to outside is connected between the fourthdischarge line and the second distribution line.
 16. The system of claim15, wherein the fourth discharge line is provided with an evaporator forevaporating water discharged from the fourth discharge line.
 17. Amethod for controlling a fuel cell system comprising: driving a DBFC;controlling hydrogen, a byproduct generated at an anode of the DBFCafter a reaction as a preset amount; and driving a PEMFC by receivinghydrogen having an amount set in the hydrogen controlling step and thususing the hydrogen as a fuel.
 18. The method of claim 17, wherein in thestep of driving a DBFC, a step of supplying a fuel to an anode of theDBFC includes: making a fuel of an aqueous solution in a fuel tank byinjecting a power fuel and water thereto; containing electrolyte aqueoussolution in an electrolyte reservoir; pumping the fuel of an aqueoussolution and thereby supplying the anode of the DBFC with theelectrolyte aqueous solution; separating a byproduct generated at theanode after a reaction into gas and liquid; and pumping the separatedliquid and thereby supplying to the fuel tank.
 19. The method of claim18, wherein in the step of driving a DBFC, a byproduct generated at acathode of the DBFC after a reaction is supplied to the electrolytereservoir thus to be separated into gas and liquid, the electrolyteaqueous solution is supplied to the anode of the DBFC at the time ofoperating the DBFC, and the electrolyte reservoir is closed thus topurge the liquid of the electrolyte reservoir to the fuel tank at thetime of stopping the DBFC.
 20. The method of claim 17, wherein externalair is introduced into an air conduit and the air conduit is divergedinto separate first and second conduits, through which air isrespectively supplied to cathodes of the DBFC and the PEMFC.
 21. Themethod of claim 17, wherein in the step of driving a DBFC, an amount ofhydrogen generated at the anode of the DBFC after a reaction iscontrolled according to a supply amount of a fuel supplied to the anode.22. The method of claim 17, wherein the step of controlling hydrogenincludes: respectively measuring an inlet pressure and an outletpressure of a hydrogen reservoir, the inlet pressure being measuredwhere hydrogen generated at the anode of the DBFC is introduced thus tobe stored, and the outlet pressure being measured where the storedhydrogen is supplied to an anode of the PEMFC; comparing the inletpressure and the outlet pressure; and continuously supplying hydrogengenerated at the anode of the DBFC to the hydrogen reservoir when theinlet pressure is greater than the outlet pressure, and shielding ahydrogen supply to the hydrogen reservoir when the inlet pressure isless than the outlet pressure.
 23. The method of claim 17, wherein thestep of controlling hydrogen includes: measuring an outlet pressure of ahydrogen reservoir, the outlet pressure being measured where hydrogengenerated at the anode of the DBFC and introduced to the inlet of thehydrogen reservoir is supplied to the anode of the PEMFC; measuring apurge cell voltage (PCV) of the PEMFC; shielding a hydrogen supply fromthe hydrogen reservoir to the PEMFC when the outlet pressure is lessthan a preset value, and comparing the PCV with a preset value when theoutlet pressure is more than the preset value; and shielding a hydrogensupply from the hydrogen reservoir to the PEMFC when the PCV is greaterthan the preset value, and shielding a hydrogen supply from the hydrogenreservoir to the PEMFC after a preset time lapses when the PCV is lessthan or the same as the preset value.
 24. The method of claim 17,further comprising measuring an oxygen concentration and a hydrogenconcentration of outside of the fuel cell system while the fuel cellsystem is operated, and displaying a visual or an audible warning whenthe measured oxygen or hydrogen concentration is more or less than apreset value and stopping the fuel cell system.
 25. The method of claim17, further comprising charging a supplementary batter using a part ofelectric energy generated between the DBFC and the PEMFC, and displayinga visual or an audible warning when a charged value of the supplementarybattery is more than a preset value so as to stop the charging.
 26. Themethod of claim 24, wherein the step of stopping the fuel cell systemincludes: stopping the DBFC, and then driving the PEMFC by hydrogenremaining between the DBFC and the PEMFC; recollecting a fuel and abyproduct remaining between the DBFC and a fuel tank to the fuel tank byelectric energy generated at the PEMFC; measuring hydrogen remainingbetween the DBFC and the PEMFC, continuously driving the PEMFC when themeasured value is more than a preset value and charging a supplementarybattery with the generated electric energy, and stopping the PEMFC whenthe measured value is less than or the same as the preset value.
 27. Themethod of claim 26, wherein the PEMFC is stopped after being operatedfor a preset time.
 28. The method of claim 26, wherein in the step ofrecollecting a fuel and a byproduct remaining between the DBFC and afuel tank to the fuel tank by electric energy generated at the PEMFC,electric energy charged at the supplementary battery is used when thePEMFC is stopped due to a deficiency in a remaining amount of hydrogen.